1. Field of the Invention
The present invention relates to a light-sensitive composition including new compounds capable of generating free radicals when they are irradiated with light and more particularly to a light-sensitive composition containing 4,6-bis(halomethyl)-s-triazines as a free radical generator.
2. Description of the Prior Art
Compounds which generate free radicals when they are irradiated with light (free radical generator) have been well known in the field of graphic art. These compounds have widely been used as a photopolymeriziation initiator in photopolymerizable compositions, as a photoactivator in free radical photographic compositions and as a photoinitiator in the reactions which are catalized with acids generated by irradiating the initiator with light. With the use of such a free radical generator, there has been produced a variety of light-sensitive materials useful in the image forming systems for printing, reproduction, duplication or the like.
Organic halogen compounds causes photolytic degradation to form free radicals of halogen such as chlorine free radicals and bromine free radicals. These free radicals of halogen serve as a good hydrogen atom extracting agent and form acids if a hydrogen donor coexists therewith. These photopolymerization processes and the application thereof to the free radical photographic processes are disclosed in the article of J. Kosar (Light Sensitive System, J. Wiley & Sons, New York, 1965, pp. 180-181 and pp. 361-370).
Typical examples of compounds which can generate free radicals of halogen by the action of light and have conventionally been known are carbon tetrachloride, iodoform and tribromoacetophenone and these compounds have widely been utilized in the aforementioned fields. However, these free radical generators cause sublimation and give out a bad smell and therefore, the use thereof leads to the reduction of its effect because of their sublimation during producing, using and storing the light-sensitive materials and the sublimation is detrimental to health. Moreover, they are incomplete in the compatibility with other components incorporated in a light-sensitive layer. Furthermore, they are less sensitive to photolytic degradation with light from a light source such as metal halide lamps commonly used in producing, for instant, a lithographic printing plate and therefore, it is required to incorporate a large amount thereof into the light-sensitive layer in order to attain a sufficient effect. Thus, it is common that the use of a large amount of these compounds exerts a great influence on mechanical properties and development properties of the light-sensitive layer containing the same.
Under such circumstances, there has been proposed the use of vinyl-halomethyl-s-triazine (U.S. Pat. Nos. 3,954,475 and 3,987,037 and Japanese Patent Unexamined Published Application, hereunder referred to as --J.P. KOKAI--, No. 48-36281); and halomethyl-s-triazine compounds (J.P. KOKAI Nos. 53-133428 and 55-32070). These s-triazine compounds surely have excellent properties such as extremely high sensitivity to photolytic degradation with ultraviolet light commonly used and high stability with time. However, when these compounds are used as a component of, for instance, light-sensitive compositions for presensitized plates for use in making lithographic printing plates (hereunder referred to as PS plate(s) for simplicity), a part of the light-sensitive composition existing in non-image areas even after development is liable to remain. In particular, if the development is carried out by rubbing the light-sensitive layer with adsorbent wadding or sponge containing developing liquid, the light-sensitive composition partially remains in non-image areas, which results in the bad appearance because of nonuniform development and leads to the generation of scumming when the resultant product is used as a lithographic printing plate.